Heater and A/C Control Assembly

HEATER AND A/C CONTROL ASSEMBLY

HVAC Control Assembly:

The electronic heater and A/C control assembly is the vehicle operator's control point for the electronic air conditioning system. The heater and A/C control assembly includes soft-touch buttons for the various system operating modes (OFF, MAX A/C, NORM A/C, BI-LEVEL, VENT, HEATER, DEFOG, DEFROST), a blower speed control, and a temperature control lever.
Vehicles equipped with a rear window defogger also have the system's ON/OFF switch located in the heater and A/C control assembly. Each operating mode button contains an LED indicator that illuminates when selected. The rear window defogger button also contains an LED indicator.
The heater and A/C control assembly is the electronic air conditioning systems "brain"; it sends commands to system components that control A/C compressor operation, air discharge location, air discharge temperature and blower operation.

A/C SOLENOID SWITCH ASSEMBLY
The A/C solenoid switch assembly operates vacuum actuators to control air intake and discharge locations. Inside the A/C solenoid switch assembly are 4 solenoid-actuated vacuum valves that respond to the heater and A/C control assembly electrical signals. The vacuum valves, in turn, vent or apply vacuum to the vacuum actuators. By energizing various valve combinations, the heater and A/C control assembly can control whether air is directed to the floor outlets, panel outlets or defroster outlets. It also determines whether fresh (outside) air is drawn into the system or inside air is recirculated.

HEATER AND A/C MODULE
The heater and A/C module is where all system air is heated, cooled, mixed together and directed to the various ducts and vents. The module consists of a housing with inlet openings, outlet openings, air passages and air valves. Vacuum actuators and an electric motor (mounted to the side of the case) operate the air valves according to the A/C solenoid switch assembly signals.

BLOWER SPEED RELAY
When energized by the heater and A/C control assembly, the blower speed relay applies voltage to both the blower switch (part of the heater and A/C control assembly) and the blower resistors to enable the blower motor.

BLOWER SWITCH
The blower switch (part of the heater and A/C control assembly) control blower speed. Blower switch position determines whether current flows to the blower resistors or the high speed blower relay.

BLOWER RESISTORS
The blower resistors make an assembly which contains 3 separate resistors. Blower speed is regulated by routing current through none, 1, 2 or all 3 resistors. The blower switch position (in the heater and A/C control assembly) determines how many resistors are bypassed.

HIGH SPEED BLOWER RELAY
When energized by the blower switch, the high speed blower relay allows current to flow directly from the RH underhood fuse block to the blower motor. With all resistors bypassed, the blower runs at high speed.

BLOWER MOTOR
The blower motor is a DC motor whose speed is proportional to the input voltage. With low voltage the motor turns at a low speed; with high voltage the motor turns at high speed.

TEMPERATURE VALVE ACTUATOR
The A/C temperature valve actuator follows commands from the temperature lever in the heater and A/C control assembly to control outlet temperature. A reversible DC motor in the actuator operates the air mix valve, which blends cooled and heater air.

VACUUM ACTUATORS
The vacuum actuators are vacuum servos that operate valves inside the case. Three actuators are used: 2 single-diaphragm actuators and one double-diaphragm actuator. The actuators are mounted to the case and are connected to the solenoid switch by vacuum hoses.